Benzoyl peroxide and its derivatives form a family of useful initiators used widely in the polymer and plastics industry. For example, such peroxides catalyze the polymerization of styrene, vinyl chloride, and the like, and the cross-linking of unsaturated polyester compositions. Dry peroxides of this family are shock sensitive and flammable. If a small amount of water is added, e.g., up to 30% by weight, the granules will remain free-flowing and solid and the safety hazards are substantially reduced. It is also possible to add inert plasticizers to reduce the danger in handling and commercial pastes comprising 50 or 55% by weight of the peroxide in tricresyl phosphate or in phthalate esters are now widely available; these can contain up to 15% by weight of water, too. See, generally, U.S. Pat. Nos. 2,454,254; 3,324,040; 3,520,825; 3,957,683. A common problem with peroxide pastes is their tendency to separate physically into their components during storage.
In U.S. Pat. No. Re. 28,818, it is proposed to stabilize such compositions by adding a small, effective amount of an expensive hydrophobic alkyl group-containing silica. Unfortunately, such compositions, while non-separating, must be very carefully prepared or they will either be non-pourable or pasty. They can, therefore, be difficult to pump and package, on the one hand, and not amenable to easy mixing with curable polyester compositions, on the other. In U.S. Pat. No. 3,731,791, creamy catalyst pastes are described comprising benzoyl peroxide, dimethyl phthalate, ground calcite (CaCO.sub.3) passing a 300 mesh B.S. sieve and the plasticizer, di-2-ethylhexyl phthalate. These patents are all incorporated herein by reference.
A system has now been discovered whereby a highly plasticized peroxide paste can be made stable, non-separating, pumpable and mixable. Moreover, the paste, which is based on the use of a minor proportion of water added alone or in combination with a plasticizer has a unique, very creamy texture.